2. Meanwhile, into same skillet, add mushrooms, onions and remaining 2 tablespoons oil. Cover and cook over medium heat 8 to 10 minutes or until most liquid is released from mushrooms. Stir in remaining 1/2 teaspoon salt and 1/4 teaspoon pepper. Stir in flour and remove skillet from heat.

3. Lay 12x18-inch sheet of plastic wrap on work surface. In center of plastic wrap, lay ham slices, overlapping slightly to form 12x14-inch rectangle. Evenly spread mushroom mixture over ham. Brush outside of beef with mustard and place beef lengthwise in center over mushroom layer. Using plastic wrap, roll ham and mushroom mixture over top and bottom of beef, leaving ends of beef uncovered. Refrigerate 15 minutes.